How far behind should you stay from another vehicle in traffic?

The universally accepted answer to this is:

2 seconds in normal driving conditions (good weather & dry roads)

and

5 seconds in inclement weather (ie: snow and icy roads).

Pick a stationary object by the side of the road (such as a telephone or hydro pole) and use it as the guage of measure. When yhr vehicle ahead passes it (lets use the pole), say out loud " 1, one thousand, 2, onethousand". you should have finished saying that before you reach the same pole or other marker.